This invention relates to a lubricating oil supplying system for an engine and more particularly to an improved arrangement for supplying an accurate and appropriate amount of lubricant to the engine during all of its running phases.
Various systems have been proposed for lubricating internal combustion engines and proposals have been made for supplying lubricant to two cycle engines for their operation. It is desirable to be able to accurately control the amount of lubricant supplied to a two cycle engine since, as is well known, any lubricant which is not used in the lubrication of the engine will pass from the exhaust and can cause problems with emission control as well as creating undesired exhaust smoke.
It has been proposed to employ a pump for pumping the lubricant to the engine, which pump is driven in timed sequence with the engine output shaft. These pumps generally are of the reciprocating type and deliver a finite amount of lubricant during each pumping stroke. In order to control the amount of lubricant supplied by such pumps, various arrangements have been incorporated,for, in effect, controlling the stroke of the pump during its operation. However, these types of lubricant flow controls make the lubricant pumps quite expensive and, in many instances, are not fully able to provide accurate control for the lubricant under all running conditions.
There has, therefore, been proposed a type of control which permits the pump to pump a full amount of lubricant each of its strokes but wherein the lubricant is selectively delivered either to the engine or bypassed back to the tank through a two-way solenoid operated valve. The amount of lubricant actually supplied to the engine is controlled by varying the duty ratio of the valve. The duty ratio is defined as the time in which the pump is delivering lubricant divided by the total operating time of the pump. Such an arrangement is disclosed in the co-pending application entitled "Lubricating Oil Supplying System for Two Cycle Engine," Ser. No. 07/862,984, filed Apr. 7, 1992 in the name of Yoshinobu Yashiro, and assigned to the assignee hereof. This invention relates to an improvement in that type of arrangement and specifically to improved control routines for controlling the duty cycle and time of pump delivery to control the amount of lubricant delivered to the engine.
FIG. 1 is a graphical view which also appears in the aforenoted co-pending application and which illustrates one of the problems with the prior art type of device wherein the plunger stroke of the lubricant pump is varied corresponding to engine speed and accelerator position. The curve "a" shows the manner in which the stroke of the pump is changed in response to engine speed changes while the curve "b" shows the actual delivery output from the pump. However, if the accelerator of the engine is opened rapidly, then the curve "c" results which provides a substantial increase in the amount of lubricant before the engine speed has actually increased. This results in excess lubricant which, at the minimum, will cause excessive hydrocarbons in the exhaust and at the maximum can additionally cause smoke to develop in the exhaust.
The aforenoted application, as discussed above, provides an arrangement wherein the pump output is controlled by varying the duty cycle of the flow controlling valve to obtain more accurate control over the amount of lubricant supplied. However, it is important to ensure that the amount of lubricant actually supplied to the engine is accurately controlled so that excess lubricant is not supplied and also so that sufficient lubricant is supplied.
It is, therefore, a principal object of this invention to provide an improved arrangement for lubricating an engine and a method for controlling the amount of lubricant supplied to the engine.
One particular problem with the control of lubricant is, as above noted, transient conditions. That is, when the engine is running at a given speed and at a given load, it is possible to accurately determine its lubricant requirements and to supply the appropriate amount of lubricant. However, when the engine speed is changed after the lubricant supply amount is determined, the amount of lubricant supplied can be incorrect.
It is, therefore, a still further object of this invention to provide an improved lubricant system and method of controlling the amount of lubricant supplied to an engine so as to accommodate transient conditions.
In conjunction with the control of fuel supplied to an engine by employing a two-way valve as aforenoted, the flow of lubricant during the time when the valve is being switched between its positions is not as great as when the valve is in its fully opened position. That is, the flow does not follow a square line shape, but rather has curved shape delivery during the opening and closing phases. As a result, the supply of lubricant does not vary completely linearly with the duty cycle of the solenoid valve. This can give rise to variations in the amount of lubricant supplied for a given condition.
It is, therefore, a still further object of this invention to provide an improved lubricant supply system and method of controlling lubricant flow wherein variations in flow in response to changes in characteristics are minimized.
The variations in lubricant supplied can be minimized if the amount of lubricant supplied to the engine is controlled primarily by extending the length of time when the valve is in its fuel delivery position rather than increasing the frequency of opening of the valve. However, if the time of lubricant delivery is the only variable that is employed in controlling the amount of lubricant, then the system may not be responsive enough under transient conditions.
It is, therefore, a still further object of this invention to provide an improved lubricant supply system for an engine which minimizes variations due to the operation of the valve but which also can respond quickly, when desired.
In connection with the supply of lubricant to an engine, it is possible to generate a three dimensional map that will indicate the actual lubricant requirements of an engine for each speed and load condition. If such a map is employed for the control strategy of the lubricant, then extremely accurate lubricant control can be achieved. However, if attempts are made to control the lubricant supply solely by controlling the amount of lubricant supplied for the engine during each cycle of operation of the pump, then the system becomes extremely complicated and it is not possible with such systems to provide the proper lubricant under all running conditions.
It is, therefore, a still further object of this invention to provide an arrangement for controlling the amount of lubricant supplied to an engine and a method therefor employing a map wherein the map is configured so as to permit accurate control of the total lubricant supplied to the engine under all running conditions with a relatively simple control strategy.